The invention relates to water-soluble copolymers, a process for their preparation, and their use as fluidizers in suspensions of solid matter.
More specifically, the invention relates to novel water-soluble copolymers of N-vinylamides with monomeric addition products of amines, amino acids, amino groups containing aromatic sulfonic acids, amino alcohols to maleic anhydride as well as maleic esters of polyoxyalkyleneglycols or their monoethers. Preferred copolymers include those which are obtained by radical copolymerization of N-vinyllactams with the above mentioned maleic acid adducts at a molar ratio of 1:1.
Fluidizers have been commonly used in conjunction with solid matter suspensions, and building or construction materials such as cement and cement mortar. Freshly prepared concrete, for example, is generally considered to be a mixture containing cement, mixing water and the additives sand and gravel of distinct particle size distribution. In contrast to concrete, a cement mortar contains no coarse additives (e.g., gravel), but often has a higher cement content.
After mixing, concrete passes several stages of development; i.e., from freshly prepared concrete to solid concrete. These stages may be partly influenced by particular additives.
Concrete additives are added to freshly prepared concrete and freshly prepared mortar and generally dissolved in the mixing water, in order to influence the workability and final characteristics thereof. Depending on the purpose of a building or of a construction part, as well as any other specific requirements, the characteristics of the concrete will have to be defined by the engineer. The most important characteristic with freshly prepared concrete are the workability, the inner cohesion and its consistency. In the case of solid concrete, the tensile and compressive strengths, resistance to frost, resistance to dew salt, waterproofness, resistance to abrasion and chemical durability are important.
All these characteristics are dependent on the water cement value (water cement factor). The water cement value (w): EQU w=W/Z;
is obtained from the quantitative ratio of water (W) to cement (Z) in freshly mixed concrete. With increasing water content the water cement value rises, and with increasing cement content it becomes smaller. A low water cement value affords better characteristics of the solid concrete and solid mortar.
On the other hand, a higher water cement value provides better workability of freshly prepared concrete. The transfer of freshly prepared concrete from a concrete mixer into the (concrete) form, and the subsequent solidification in the (concrete) form requires a considerable consumption of work and control of work. Therefore, a considerable difference in cost has arisen depending on the workability of a particular batch.
In order to reduce expenditures on work and cost, concrete mixtures have been made more liquid by adding more mixing water (which increases the water cement value). Unfortunately, this has always resulted in reduced strength for the hardened concrete. In recent years so-called fluidizers (also frequently referred to as super plasticizers or heavy duty plasticizers) have been increasingly used which allow for an improvement in the consistency of a concrete mixture at a constant water cement value.
Water reducing agents based on polycondensates such as the sodium or calcium salts of sulfonated naphthalene formaldehyde condensates described in U.S. Pat. No. 3,537,869, or salts of sulfonated melamine formaldehyde condensates such as those described in DE-PS 1 671 017, have been used as super plasticizers in order to improve the workability and the time-dependent flow behavior of cement mortars and concrete. These water reducing agents can improve the flowability of such mixtures, but this flowability may not be maintained according to normal practice for a sufficiently long period of time. As a result, additional amounts of water reducing agents have to be added at certain intervals.
Copolymers based on acrylic acid which show a stronger influence on flowability have been tried as super plasticizers. Unfortunately, these compounds have the drawback of significantly retarding development strength when added in the usual dosages to mortar or concrete. They have yet to be established on the market.
Water reducing agents have also been used in the production of gypsum building materials such as gypsum board. Gypsum is the generic name for the mineral (hydrous calcium sulfate, CaSO.sub.4.2H.sub.2 O) variously known as selenite, satin spar, alabaster, rock gypsum, gypsite, etc., and is commonly used to make a form of plaster.
In the production of gypsum sheet materials (e.g., gypsum board which is a gypsum plaster board covered with paper), sheet products are normally fabricated on a high-speed machine that automatically spreads a foamy plaster core between sheets of tough surface papers, and cuts the resultant board to proper dimensions. In the past, water reducing agents have been added to plaster solutions to ease processing. These agents have commonly been formaldehyde-based water reducing agents.
Formaldehyde, unfortunately, is toxic (e.g., by inhalation) and its handling and containment constitutes a tremendous practical problem during the production of gypsum materials. For example, formaldehyde is released to the air when gypsum board is dried.
It is generally known that N-vinyllactams such as 1-ethenyl-2-pyrrolidinon, may be copolymerized in solution with a large number of olefinic group containing monomers. Many of these products may be used as water-soluble polymeric dispersing agents. For example, U.S. Pat. No. 3,116,254 describes a copolymer with maleic anhydride and its alkali metal salts obtained by hydrolysis, and its use as a fluidizers for hydraulic cement compositions.
DE-OS 35 29 095 describes preparing copolymers with acrylic acid which are used as auxiliary products for building materials, especially as additives for flow mortars.
GB-PS 2 202 526 describes ternary copolymers with acrylamide and Na-2-acrylamido-2-methylpropanesulfonate. European Patent Application No. 0,116,671 describes copolymers of vinyl- and allyl sulfonic acids.